Conventionally, for the purpose of reducing a shred size of paper shredder waste pieces (shredder dust), there has been developed a shredder which strip-cuts paper into a plurality of parallel pieces and then further cross-cuts the pieces. In Japanese Examined Utility Model Application Publication No. 48-13990, pull-in rollers are provided on a discharge side of a strip-cut shredding portion and the pull-in rollers tear the strip-cut waste pieces discharged from the strip-cut shredding portion. However, tearing does not result in the constant shred size and some types of paper cannot be torn. Therefore, a shredder as shown in Japanese Unexamined Patent Application Publication No. 2002-18302 and including a cross-cut shredding portion on a discharge side of a strip-cut shredding portion is employed at present.
FIG. 3 illustrates a main part of a conventional paper shredder. The shredder includes a strip-cut shredding portion 10 that engages paired disc-shaped multi-plate rotary cutters 11, 12 with each other to strip-cut paper P passing through the engaged portion into many long and narrow noodle shaped strip-cut waste pieces Q1 with predetermined widths, each of the cutters 11, 12 having a large number of disc-shaped cutters disposed on a rotary drive shaft, and a cross-cut shredding portion 20 that has a spiral rotary cutter 21 with spirally-arranged shredding blades and a flat-blade cross-cut fixed cutter 22 facing the spiral rotary cutter 21 and which further finely cross-cuts (chops) the strip-cut waste pieces Q1 discharged from the strip-cut shredding portion 10. The strip-cut shredding portion 10 and the cross-cut shredding portion 20 as main parts form a shredding mechanism.
According to this shredder, the noodle-shaped strip-cut waste pieces Q1 discharged from the strip-cut shredding portion 10 are normally cross-cut when cutting edges of the spiral rotary cutter 21 of the downstream cross-cut shredding portion 20 pass by the cross-cut fixed cutter 22 due to rotation, and rectangular shredder waste pieces Q2 are discharged as illustrated in FIG. 3. Lengths of the shredder waste pieces Q2 are determined based on a feed speed by the disc-shaped multi-plate rotary cutters 11, 12, a rotating speed of the spiral rotary cutter 21, and the number of blades of the spiral rotary cutter 21.
In the above described structure, when the noodle shaped strip-cut waste pieces Q1 are then shredded into the rectangular shredder waste pieces Q2, base end sides (upper sides) of the strip-cut waste pieces Q1 are held by the engaged portion of the paired disc-shaped multi-plate rotary cutters 11, 12 of the strip-cut shredding portion 10 (FIG. 3). However, at a final shredding stage of the paper P, as illustrated in FIG. 4, final strip-cut waste pieces (hereinafter referred to as “final cut waste pieces”) Q3 after completion of strip cutting of a remaining part of the paper are freed from the strip-cut shredding portion 10 and drop without being cross cut as soon as the base ends of the pieces Q3 (an upper edge of the paper P) separate from the engaged portion.
Therefore, from the conventional shredder, the final cut waste pieces Q3 are discharged as the waste pieces longer than the shredder waste pieces Q2 discharged before. To put it concretely, the final cut waste pieces Q3 have lengths corresponding to distance X1 from the engaged portion of the paired disc-shaped multi-plate rotary cutters 11, 12 to the cutting edge of the fixed cutter 22 in FIG. 4 and are twice the shredder waste pieces Q2 discharged before or greater in length.
As described above, the shred size at the final stage of the shredding is large in the conventional shredder, which increases a volume of the entire shredder waste. The increase in the shred size may affect confidentiality of these parts of the paper.